Schema level diagrams support
the fact that one Express schema can interface other schemas. We
distinguish between single and
multiple schema level
diagrams. A single level schema
diagram represent only the tops level of the interfaced schemas. A multi level schema diagram is able
to show the complete dependencies of many interacting schemas.
In the Entity level diagrams all the
data types such as entities, defined types with all their relations and
attributes, are displayed.
Express schemas
can be handled in two different
ways:
Short
form - this is the default one and covers the EXPRESS Schema as
it is
written with all the references to other schemas (USE FROM, REFERENCE
FROM).
Long from
- here the schema is
flattend - all the REFERENCE FROM and USE FROMS are removed and
replaced by the interfaced types.
In layout mode a schema may be
represented only partially or completely.
For reference purpose a complete graphical layout with all details is
typically needed. For explanatory purposes however it is desired to
draw only the main objects and relations, but skip less important
details.